U.S. patent application number 11/633692 was filed with the patent office on 2008-06-05 for amplified flow through pressure sensor.
This patent application is currently assigned to Honeywell International Inc.. Invention is credited to Saravanan Sadasivan, Thirumani A. Selvan.
Application Number | 20080127741 11/633692 |
Document ID | / |
Family ID | 39402799 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080127741 |
Kind Code |
A1 |
Selvan; Thirumani A. ; et
al. |
June 5, 2008 |
Amplified flow through pressure sensor
Abstract
A MEMS based pressure sensor for flow measurements includes a
pressure sense die located between a media seal and a conductive
seal. Such a system includes a pressure sense die located between a
media seal and a conductive seal. A sensing diaphragm is generally
associated with the pressure sense die, wherein the sensing
diaphragm deflects when a pressure is applied thereto. An impedance
circuit is generally embedded with one or more resistors on the
sensing diaphragm to which the pressure to be detected is applied.
An ASIC is generally associated with the impedance circuit and the
sense die, wherein the ASIC is placed on a lead frame for signal
conditioning in order to detect a change in the pressure.
Inventors: |
Selvan; Thirumani A.;
(Bangalore, IN) ; Sadasivan; Saravanan;
(Bangalore, IN) |
Correspondence
Address: |
Attorney, Intellectual Property;Honeywell International Inc.
101 Columbia Rd., P.O. Box 2245
Morristown
NJ
07962
US
|
Assignee: |
Honeywell International
Inc.
|
Family ID: |
39402799 |
Appl. No.: |
11/633692 |
Filed: |
December 4, 2006 |
Current U.S.
Class: |
73/727 ;
702/138 |
Current CPC
Class: |
H01L 2224/48091
20130101; H01L 2924/3011 20130101; H01L 2924/1461 20130101; H01L
2924/10253 20130101; H01L 2224/48091 20130101; H01L 2924/10253
20130101; H01L 2924/00 20130101; H01L 2924/00 20130101; H01L
2924/00 20130101; G01F 1/383 20130101; H01L 2924/00014 20130101;
H01L 2924/1461 20130101; H01L 2924/3011 20130101 |
Class at
Publication: |
73/727 ;
702/138 |
International
Class: |
G01L 9/06 20060101
G01L009/06 |
Claims
1. A MEMS based pressure sensing system for flow rate measurements,
comprising: a sensor partitioned into a first half and a second
half, with a wall member separating said first half and said second
half; a pressure block comprising a sensing diaphragm associated
with a piezoresistive material, wherein said sensing diaphragm
deflects when a pressure is applied to said piezoresistive
material; a first signal conditioning unit arranged in said first
half of said sensor, wherein said first signal conditioning circuit
comprises an impedance circuit embedded with at least one
piezoresistive element associated with said piezoresistive
material; and a second signal conditioning unit arranged in said
second half of said sensor, wherein said second signal conditioning
unit incorporates a signal amplifier, such that said first and
second signal conditioning units, said pressure block, said sensing
diaphragm and said sensor provide a MEMS based pressure sensing
system for flow rate measurements.
2. The system of claim 1 wherein said signal amplifier comprises an
ASIC.
3. The system of claim 1 further comprising: a conductive
elastomeric pad positioned within said first half; a pressure
sensor positioned on said conductive elastomeric pad; an
elastomeric media seal positioned on said sensor; a flow through
tube located on said elastomeric media seal, wherein said flow
through tube is attached to a housing such that a flow through said
flow tube and said housing together form a hermetic seal by snap
fit, which prevents an escape or an entry of fluid through said
hermetic seal, wherein said flow through said flow tube follows a
path for admitting a fluid under pressure into said first half;
4. The system of claim 3 further comprising an electrical connector
through said wall member thereby forming an electrical connection
between said sensor and said signal amplifier.
5. The system of claim 3 further comprising a lead frame comprising
a plurality of electrical connectors extending through said
housing, wherein said lead frame forms an electrical connection
with said sensor and said signal amplifier.
6. The system of claim 1 wherein said sensor comprises a
piezoresistive pressure sensor.
7. The system of claim 1 wherein said impedance circuit comprises a
four-resistor Wheatstone bridge fabricated on a single monolithic
die utilizing micromachining technology.
8. The system of claim 1 wherein said first signal conditioning
unit on excitation produces a signal output.
9. The system of claim 2 wherein said ASIC comprises: a
programmable gain amplifier (PGA) for pre-amplifying a bridge
sensor signal generated by a bridge sensor; a multiplexer (MUX)
connected to said PGA, wherein said MUX transmits said bridge
sensor signal from said bridge sensor; an analog-to-digital
converter (ADC) connected to said MUX, wherein said ADC converts
said bridge sensor signal from said MUX into at least one digital
value; a calibration microcontroller (CMC) connected to said ADC,
wherein said CMC provides a digital signal correction to said at
least one digital value generated by said ADC; a ROM connected to
said CMC, wherein said ROM stores a special correction formula; an
EEPROM connected to said CMC, wherein said EEPROM calibrates
correction equation coefficients; a digital-to-analog converter
(DAC) for converting a final value output from said CMC into an
analog voltage; and a serial interface (SIF) connected to said
EEPROM, wherein said SIF provides an output signal.
10. The system of claim 9 wherein said SIF programs configuration
data and correction parameters into said EEPROM.
11. A MEMS based pressure sensing system for flow rate
measurements, comprising: a sensor partitioned into a first half
and a second half, with a wall member separating said first half
and said second half, wherein said sensor comprises a
piezoresistive pressure sensor; a pressure block comprising a
sensing diaphragm associated with a piezoresistive material,
wherein said sensing diaphragm deflects when a pressure is applied
to said piezoresistive material; a first signal conditioning unit
arranged in said first half of said sensor, wherein said first
signal conditioning circuit comprises an impedance circuit embedded
with at least one piezoresistive element associated with said
piezoresistive material; and a second signal conditioning unit
arranged in said second half of said sensor, wherein said second
signal conditioning unit incorporates a signal amplifier, wherein
said signal amplifier comprises an ASIC, such that said first and
second signal conditioning units, said pressure block, said sensing
diaphragm and said sensor provide a MEMS based pressure sensing
system for flow rate measurements
12. The system of claim 11 further comprising: a conductive
elastomeric pad positioned within said first half; a pressure
sensor positioned on said conductive elastomeric pad; an
elastomeric media seal positioned on said sensor; a flow through
tube located on said elastomeric media seal, wherein said flow
through tube is attached to a housing such that a flow through said
flow tube and said housing together form a hermetic seal by snap
fit, which prevents an escape or an entry of fluid through said
hermetic seal, wherein said flow through said flow tube follows a
path for admitting a fluid under pressure into said first half;
13. The system of claim 12 further comprising an electrical
connector through said wall member thereby forming an electrical
connection between said sensor and said signal amplifier.
14. The system of claim 12 further comprising a lead frame
comprising a plurality of electrical connectors extending through
said housing, wherein said lead frame forms an electrical
connection with said sensor and said signal amplifier.
15. The system of claim 11 wherein said impedance circuit comprises
a four-resistor Wheatstone bridge fabricated on a single monolithic
die utilizing micromachining technology.
16. The system of claim 11 wherein said first signal conditioning
unit on excitation produces a signal output.
17. The system of claim 11 wherein said ASIC comprises: a
programmable gain amplifier (PGA) for pre-amplifying a bridge
sensor signal generated by a bridge sensor; a multiplexer (MUX)
connected to said PGA, wherein said MUX transmits said bridge
sensor signal from said bridge sensor; an analog-to-digital
converter (ADC) connected to said MUX, wherein said ADC converts
said bridge sensor signal from said MUX into at least one digital
value; a calibration microcontroller (CMC) connected to said ADC,
wherein said CMC provides a digital signal correction to said at
least one digital value generated by said ADC; a ROM connected to
said CMC, wherein said ROM stores a special correction formula; an
EEPROM connected to said CMC, wherein said EEPROM calibrates
correction equation coefficients; a digital-to-analog converter
(DAC) for converting a final value output from said CMC into an
analog voltage; and a serial interface (SIF) connected to said
EEPROM, wherein said SIF provides an output signal.
18. The system of claim 17 wherein said SIF programs configuration
data and correction parameters into said EEPROM.
19. A MEMS based pressure sensing system for flow rate
measurements, comprising: a sensor partitioned into a first half
and a second half, with a wall member separating said first half
and said second half; a pressure block comprising a sensing
diaphragm associated with a piezoresistive material, wherein said
sensing diaphragm deflects when a pressure is applied to said
piezoresistive material; a first signal conditioning unit arranged
in said first half of said sensor, wherein said first signal
conditioning circuit comprises an impedance circuit embedded with
at least one piezoresistive element associated with said
piezoresistive material, wherein said impedance circuit comprises a
four-resistor Wheatstone bridge fabricated on a single monolithic
die utilizing micromachining technology, such that said first
signal conditioning unit on excitation produces a signal output;
and a second signal conditioning unit arranged in said second half
of said sensor, wherein said second signal conditioning unit
incorporates a signal amplifier, such that said first and second
signal conditioning units, said pressure block, said sensing
diaphragm and said sensor provide a MEMS based pressure sensing
system for flow rate measurements.
20. The system of claim 19 further comprising: a conductive
elastomeric pad positioned within said first half; a pressure
sensor positioned on said conductive elastomeric pad; an
elastomeric media seal positioned on said sensor; a flow through
tube located on said elastomeric media seal, wherein said flow
through tube is attached to a housing such that a flow through said
flow tube and said housing together form a hermetic seal by snap
fit, which prevents an escape or an entry of fluid through said
hermetic seal, wherein said flow through said flow tube follows a
path for admitting a fluid under pressure into said first half; an
electrical connector through said wall member thereby forming an
electrical connection between said sensor and said signal
amplifier; and a lead frame comprising a plurality of electrical
connectors extending through said housing, wherein said lead frame
forms an electrical connection with said sensor and said signal
amplifier.
Description
TECHNICAL FIELD
[0001] Embodiments are generally related to sensor methods and
systems. Embodiments are also related to MEMS
(Microelectromechanical System) based pressure sensors. Embodiments
are additionally related to pressure sensors that incorporate ASIC
(Application Specific Integrated Circuit) components for signal
conditioning and/or amplification.
BACKGROUND OF THE INVENTION
[0002] Many processes and devices have been used for measuring flow
rate in different applications. A miniature MEMS based pressure
sensor can be used to measure very low flow rates and with a
reliable accuracy. Such MEMS based pressure sensors have been
implemented, for example, in various flow sensing devices, such as
medical applications, some of which utilize silicon piezoresistive
sensing technology for measuring very low pressures. Other flow
sensing implementations, for example, include environmental
applications.
[0003] MEMS involve the integration of micro-mechanical elements,
sensor actuators, and electronic components on a common silicon
substrate through the use of microfabrication technology. While the
electronics can be fabricated using integrated circuit (IC) process
sequences (e.g., CMOS, Bipolar, or BICMOS processes), the
micromechanical components can be fabricated using compatible
"micromachining" processes that selectively etch away parts of the
silicon wafer or add new structural layers to form the mechanical
and electromechanical devices. MEMS promises to revolutionize
nearly every product category by bringing together silicon based
microelectronics with micromachining technology, making possible
the realization of complete "system-on-a-chip". MEMS is an enabling
technology allowing the development of "smart" products, while
augmenting the computational ability of microelectronics with the
perception and control capabilities of microsensors and
microactuators, while expanding the space of possible designs and
applications.
[0004] The majority of prior art MEMS pressure transducers produced
for the automotive market, for example, typically include a
four-resistor Wheatstone bridge fabricated on a single monolithic
die using bulk-etch micromachining technology. The piezoresistive
elements integrated into the sensor die can be located along the
periphery of the pressure sensing diaphragm at points appropriate
for strain measurement. Such sensors are inexpensive to produce and
can be processed in association with integrated circuits on a wafer
that may contain a few hundred to a few thousand sensing
elements.
[0005] In a bridge configuration, the resistance of diagonally
opposed legs varies equally and in the same direction, as a
function of the mechanical deformation caused by pressure. As the
resistance of one set of diagonally opposed legs increases under
pressure, the resistance of the other set decreases, and vice
versa. Bridge excitation in the form of voltage or current is
applied across two opposite corners of the bridge. Any change in
voltage (e.g., pressure) can be detected as a voltage difference
across the other two corners of the bridge, typically referred to
as signal output. Unfortunately for silicon piezoresistive sensors,
this voltage difference is quite small. Thus, the sensor must be
compensated before it can be used.
[0006] Bulk-micromachined silicon pressure sensors typically
incorporate the use of a diaphragm that deflects when subjected to
a pressure load, and also include a piezoresistive transducer that
translates strain to a differential voltage. Metal pads can be used
to interface with other system components. Signal-conditioning
circuitry for calibration or amplification is optional, but is
often included as well. The piezoresistive transducer is
strategically placed near the edge of the diaphragm, since that is
a high-strain location and each sensor is designed, such that its
output voltage is linearly proportional to the applied pressure in
its operating range.
[0007] In some applications, it is preferred that a signal
conditioning/signal amplification capability be incorporated into
the sensors. It is believed that there is currently no amplified
flow through sensors based on piezoresistive sensing technology in
an integrated package. It is further believed that if such a sensor
could be implemented, this would help in lowering installation and
development costs, while eliminating secondary operations and
shortening the design cycle time.
BRIEF SUMMARY
[0008] The following summary is provided to facilitate an
understanding of some of the innovative features unique to the
embodiments disclosed and is not intended to be a full description.
A full appreciation of the various aspects of the embodiments can
be gained by taking the entire specification, claims, drawings, and
abstract as a whole.
[0009] It is, therefore, one aspect of the present invention to
provide for an improved pressure sensor for measuring very low flow
rates with a reliable accuracy.
[0010] It is another aspect of the present invention to provide for
a pressure sensor that integrates an ASIC for signal conditioning
and isolates the ASIC from a pressure sensing die cavity.
[0011] It is a further aspect of the present invention to provide
for a miniature amplified and temperature compensated flow through
sensor in a single package.
[0012] The aforementioned aspects and other objectives and
advantages can now be achieved as described herein. A pressure
sensor is system and/or pressure sensing device are disclosed. Such
a device includes a housing partitioned into two halves. In one
half, a pressure sensing die with a conductive seal and a media
seal can be packaged and in the other half, an ASIC can be
provided. The ASIC is preferably placed on the lead frame so that
the temperature sensor in the ASIC is used for temperature
compensation. The whole housing can then be packaged with a top
case, which can be heat-sealed ultrasonic welded or any other
plastic joining process.
[0013] The pressure sensor can be implemented in the context of a
MEMS based pressure sensing system for flow rate measurements. Such
a system includes a pressure sense die located between a media seal
and a conductive seal. A sensing diaphragm is generally associated
with the pressure sense die, wherein the sensing diaphragm deflects
when a pressure is applied thereto. An impedance circuit is
generally embedded with one or more resistors on the sensing
diaphragm to which the pressure to be detected is applied. An ASIC
is generally associated with the impedance circuit and the sense
die, wherein the ASIC is placed on a lead frame for signal
conditioning in order to detect a change in the pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying figures, in which like reference numerals
refer to identical or functionally similar elements throughout the
separate views and which are incorporated in and form a part of the
specification, further illustrate the embodiments and, together
with the detailed description, serve to explain the embodiments
disclosed herein.
[0015] FIG. 1 illustrates exploded-perspective view of an amplified
flow through pressure sensor incorporating an ASIC, which can be
implemented in accordance with a preferred embodiment;
[0016] FIG. 2 illustrates a plan view of a flow through pressure
sensor package, which can be implemented in accordance with a
preferred embodiment;
[0017] FIG. 3-5 illustrates cross-sectional views taken along lines
A-A, B-B and C-C respectively, with respect to the illustration
depicted in FIG. 2, in accordance with a preferred embodiment;
[0018] FIG. 6 illustrates a detailed functional block diagram of a
pressure sensor incorporating an ASIC as depicted in FIG. 1, where
pressure is applied to the bottom side, in accordance with a
preferred embodiment; and
[0019] FIG. 7 illustrates a detailed functional block diagram of a
pressure sensor incorporating an ASIC as depicted in FIG. 1, where
pressure is applied to the top side, in accordance with an
alternative embodiment.
DETAILED DESCRIPTION
[0020] The particular values and configurations discussed in these
non-limiting examples can be varied and are cited merely to
illustrate at least one embodiment and are not intended to limit
the scope thereof.
[0021] FIG. 1 illustrates an exploded-perspective view of an
amplified flow through pressure sensor 100, which can be
implemented in accordance with a preferred embodiment. The
amplified flow through sensor 100 can be partitioned into two
halves, first half 101 and second half 102. A tube 103 is generally
located between and proximate to the first half 101 and second half
102. In first half 101, a pressure sense die 105 can be packaged
with a media seal 106 and a conductive seal 107. A pressure
inducing substance can flow through tube 103. In the second half
102, an ASIC 108 can be located and packaged. The sensor 100 can be
placed in a desired base with the assistance of a connector
104.
[0022] FIG. 1 further illustrates a second half 102 of the pressure
sensor 100 wherein the ASIC 108 is placed. The ASIC 108 is
generally placed on a lead frame 109 so that a temperature sensor
in the ASIC 108 is used for temperature compensation. The ASIC 108
placed on the lead frame 109 can be located on a plastic housing
110 on the second half 102 of the sensor 100. The entire sensor 100
can be heat-sealed, ultrasonic welded or joined by any other
plastic joining process. The ASIC 108 incorporated in the second
half 102 of the sensor brings about a signal amplification.
[0023] FIG. 2 illustrates a plan view 200 of the flow through
pressure sensor 100 according to a preferred embodiment. Note that
in FIGS. 1-2, identical or similar parts or elements are generally
indicated by identical reference numerals. For example, the first
half 101 and second half 102 of the sensor and the flow through
tube 103 depicted in FIG. 1 also appears in FIG. 2. The plane A-A
illustrates the horizontal cross-section of flow through pressure
sensor and the lines B-B and C-C illustrates the vertical
cross-section of the flow through pressure sensor 100. The first
half of the amplified flow through sensor 100 is illustrated by 101
and second half is illustrated by 102. The sensor 100 can be placed
in a desired base with the assistance of a connector 104, depending
upon design considerations.
[0024] FIG. 3 illustrates a cross-sectional view 300 along the
plane A-A that includes the first half 101 and second half 102 of
the amplified flow through pressure sensor 100. Note that in FIGS.
1-3, identical or similar parts or elements are generally indicated
by identical reference numerals. Thus the reference numerals 101,
102, 103, 104, 105, 106, 107, 110 as depicted in FIG. 1 refer to
the same components in FIG. 3. A pressure sense die 105 can be
packaged with a media seal 106 and a conductive seal 107. A
pressure inducing substance can flow through tube 103. The second
half 102 has a plastic housing 110 where the ASIC 108 is placed.
The sensor 100 can be placed in a desired base with the assistance
of a connector 104.
[0025] FIG. 4 illustrates a cross sectional view 400 of the
amplified flow through pressure sensor along the plane B-B. Note
that in FIGS. 1-3, identical or similar parts or elements are
generally indicated by identical reference numerals. Thus, the
reference numerals 101, 104, 105, 106, and 107 as depicted in FIG.
1 refer to the same components in FIG. 4. The figure illustrates
the first half 101 of the pressure sensor. A pressure sense die 105
can be packaged with a media seal 106 and a conductive seal 107 as
illustrated in the figure. The sensor 100 can be placed in a
desired base with the assistance of a connector 104.
[0026] FIG. 5 illustrates a cross-sectional view 500 of the flow
through sensor along the section C-C that includes the first half
101 and second half 102 of the amplified flow through pressure
sensor 100. Note that in FIGS. 1-5 identical or similar parts or
elements are generally indicated by identical reference numerals.
Thus, the reference numerals 101 and 102 as depicted in FIG. 1
refer to the same components in FIG. 4.
[0027] FIG. 6 illustrates a functional block diagram 600 of a
pressure sensor 100 with an ASIC 108 as depicted in FIG. 1
incorporated for signal conditioning and amplification when
pressure is applied on the pressure die 105, in accordance with a
preferred embodiment. Note that in FIGS. 1 and 6, identical or
similar parts and/or elements are generally indicated by identical
reference numerals. Thus reference numerals 100 and 108 depicted in
FIG. 1 refers to the same components in FIG. 6. Pressure sensor 100
generally includes a pressure block 202 in association with a first
signal conditioning unit 206, which is connected to a second signal
conditioning unit 208. The first signal conditioning unit 206
generates one or more signals that can be transmitted to the second
signal conditioning unit 208. An external supply voltage 205
provides a voltage to the first signal conditioning unit 206 and
the second signal conditioning unit 208. The pressure sensor 100
additionally includes an ASIC 108 in the signal conditioning unit
208.
[0028] As depicted by arrow 201 in FIG. 6, input pressure (P) can
be applied to the pressure block 202. This pressure change causes a
deflection of a membrane as indicated by arrow 203, and as a result
deflection to resistance change of the resistive network 204 occurs
in the signal conditioning unit 206. This process can be referred
to as "signal conditioning". The external supply voltage (Vs) 205
can be provided to the signal conditioning units 206 and 208, which
in turn produces the output signal (V.sub.o) 207, which occurs via
the first signal conditioning unit 206. The output signal 207 is
then passed to the second signal conditioning unit 208. ASIC 108
generally performs signal conditioning/amplification at the second
signal conditioning unit 208 and generates an amplified output
signal 209 (i.e., V.sub.o amplified). The sensor signal
conditioning units 206 and 208 work together to perform all
necessary functions for calibration, temperature compensation
influence and linearizing the amplified output signal 209, and thus
improvement is obtained by integrating the ASIC 108 for signal
conditioning and its isolation from the pressure block 202.
[0029] FIG. 7 illustrates a high-level block diagram 400 of a
pressure sensor 100 incorporating an ASIC 108 depicted in FIG. 1,
in accordance with a preferred embodiment. Note that in FIGS. 1-7,
identical or similar parts and/or elements are generally indicated
by identical reference numerals. Thus reference numerals 105 and
108 as depicted in FIG. 1 and reference numerals 202, 203, 204,
205, 206, 207, 208 and 209 depicted in FIG. 6 refers to the same
components in FIG. 7. As indicated by arrow 401 in FIG. 7, input
pressure can be applied to the pressure block 202. Pressure sense
die 105 senses the pressure change and causes a deflection of
membrane as indicated by the arrow 203 and as a result change in
resistance of the resistive network 204 occur in the first signal
conditioning unit 206. The signal conditioning unit 206 generates
an output signal (Vo) 207. The ASIC 108 performs signal
conditioning and amplification at the second signal conditioning
unit 208 and generates the amplified output signal (V.sub.o
amplified) 209 and corrects the output digitally. In some
implementations, the ASIC 108 can be powered by a 5 Volt DC source
(V.sub.s) 205.
[0030] Positioned within the second cavity is a signal amplifier
108 which is in electrical contact with the pressure sensor and
amplifies a signal from the pressure sensor representative of the
pressure of a fluid such as air or air and water vapor within the
first cavity. The signal amplifier is preferably an application
specific integrated circuit (ASIC), which is well known in the art.
ASIC's can also be used for signal-conditioning a MEMS silicon
piezoresistive sensor. The ASIC may be employed to calibrate and
compensate the pressure sensor with a total error of less than
.+-.1% full scale output (FSO) over its operating pressure range.
The total error includes effects due to offset and sensitivity, as
well as the offset and sensitivity temperature coefficients.
[0031] ASIC's are useful because a typical output signal for a
piezoresistive pressure sensor depends on temperature. Useful
ASIC's include, for example, ASIC devices such as the DSP-based
circuit from Fujikura Ltd. in Tohoku, Japan that may correct for
the sensor's offset and sensitivity. Such an example Fujikura's
circuit can operate in a temperature range from -30.degree. C. to
80.degree. C. The example Fujikura's ASIC can be configured on a
0.7-pm double-polysilicon, double-metal, n-well CMOS process. It
has a sigma-delta 16-bit analog-to-digital converter, a reference
voltage with a built-in temperature sensor, the 16-bit DSP core,
101 polysilicon fuses, a step-up voltage regulator, a 10-bit
digital-to-analog converter (DAC), and a 4-MHz oscillator.
Corrected coefficients are stored using the polysilicon fuses. The
output code is accessible with a serial interface or an analog
signal provided by a 10-bit DAC. This circuit also may compensate
for secondary temperature characteristics and can utilize, for
example, a 120 serial interface. A built-in charge pump permits the
device to function within circuits rated under 3 V. A "sleep" mode
reduces power consumption.
[0032] Another example of an ASIC is a device produced by The
Institute of Microelectronics in Singapore, which is a fully
customized analog ASIC with a fusible-link array that achieves the
aforementioned performance from -40.degree. C. to 125.degree. C.
Such an ASIC can be configured via a 0.8-pm double-polysilicon,
double-metal CMOS process. This type of an ASIC includes a core
analog signal processor, a 64-bit fusible link array, and a serial
fusible-link interface. The ASIC's digital portion provides the
interface between the analog signal processor and controller. This
controller writes data to an interface and reads data back from it
by a serial-in and serial-out communications protocol. Data in the
serial interface can be loaded into the fusible-link array to
control various resistor networks in the analog signal processor.
These resistor networks are used for various programmable
functions.
[0033] All of these programmable elements make it possible to
compensate for the calibration, sensitivity, and temperature
effects to the first order. The ASIC features an output of 0.5 to
4.5 V using a 5-V power supply. Other suitable signal amplifiers,
which may be adapted in accordance with alternative embodiments,
include for example, a ZMD31050 RB.sup.IC series advanced
differential sensor signal conditioner, commercially available from
ZMD America Inc, of Melville, N.Y.
[0034] The signal path of the ASIC 108 is partly analog and partly
digital. The analog part is realized differentially. Consequently,
it is possible to amplify positive and negative input signals,
which are located in the common mode range of the signal input. The
electrical output signal (V.sub.o) 207 from the signal conditioning
unit 206 can be pre-amplified by a programmable gain amplifier
(PGA) 402. A multiplexer (MUX) 403 can be utilized to transmit
signals generated by signal conditioning unit 206 or a separate
temperature sensor (TS) 404 to an analog-to-digital converter (ADC)
405 in a certain sequence. Thereafter, the ADC 405 converts these
signals to digital values. A digital signal correction takes place
in a calibration microcontroller (CMC) 406 and is based on a
special correction formula located in an ROM 407 and on
sensor-specific coefficients stored into an EEPROM 408 during
calibration.
[0035] The output signal (V.sub.o Amplified) 209 can be provided at
a serial interface (SIF) 409. The final value can be converted to
an analog voltage via an 11-bit Digital-to-Analog converter (DAC)
410. The analog output 411 possesses registers which can store the
actual pressure and the results of temperature measurement.
According to the programmed output configuration, the corrected
sensor amplified signal output (V.sub.o amplified) 209 is produced
as the analog value. The configuration data and the correction
parameters can be programmed into the EEPROM 408 via the serial
digital interfaces 409. The signal paths from pressure sense die
105 to the amplified output signal 209 (V.sub.o amplified) is
generally analog-digital-analog for isolation and compensation
flexibility.
[0036] The correction values at each temperature of calibration can
be recorded utilizing a computer. A calculation can then be
utilized to fabricate a multi-order equation that corrects the
sensor's output over temperature. The coefficients for that
equation can be loaded into the unit's EEPROM 408 after the final
calibration temperature data is taken. After the correction
equation coefficients are loaded into the unit's EEPROM 408, the
device is considered fully calibrated. The calibration procedure
should preferably include the set of coefficients of calibration
calculation and depending on the configuration, the adjustment of
the extended offset compensation, the zero compensation of
temperature measurement, and the adjustment of the bridge
current.
[0037] The pressure sensor described herein can be inexpensively
manufactured and marketed and can include temperature compensation
and calibration capabilities, along with media flow-through ports
and true "wet" differential sensing and is also operable after
exposure to frozen conditions with a choice of termination for gage
sensors. Such a sensor can also provide interchangeability, proven
elastomeric construction, ASIC based signal conditioning and
digital output and can be used to measure vacuum or positive
pressure.
[0038] The disclosed pressure sensor device and system can find
usefulness in a wide range of application, such as, for example,
medical applications, including but not limited to dental chairs,
nebulizers, kidney dialysis machines, blood cell separators and so
forth. Such products not only simplify the testing, monitoring, and
treatment process, but will also assist in improving the quality of
life for patients by minimizing time spent in hospitals and
providing automatic and continuous treatment of chronic conditions.
Such a device and/or system can also be employed in environmental
applications, such as water control valves, instrumentation,
irrigation equipment, and so forth, whenever flow monitoring and
control are important.
[0039] It will be appreciated that variations of the
above-disclosed and other features and functions, or alternatives
thereof, may be desirably combined into many other different
systems or applications. Also that various presently unforeseen or
unanticipated alternatives, modifications, variations or
improvements therein may be subsequently made by those skilled in
the art which are also intended to be encompassed by the following
claims.
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